1. Field of the Invention
The present inventions relate to cordless window shades, and spring drive systems used in cordless window shades.
2. Description of the Related Art
Many types of window shades are currently available on the market, such as Venetian blinds, roller shades and honeycomb shades. The shade when lowered can cover the area of the window frame, which can reduce the amount of light entering the room through the window and provided increased privacy. Conventionally, the window shade is provided with an operating cord that can be manually actuated to raise or lower a bottom rail of the window shade. The bottom rail can be raised by winding a suspension member around a rotary drum, and lowered by unwinding the suspension member from the rotary drum.
However, there have been concerns that the operating cord of the window shade may pose strangulation threat to children. As a result, cordless window shades have been developed, which use electric motors or spring motors to raise and lower the bottom rail. Spring motors used in window shades generally consist of springs that are operable to apply a torque for keeping the bottom rail at a desired height. However, the conventional assemblies of the spring motors are usually complex, and require multiple moving parts to transmit the spring torque to the rotary drum. This may increase the weight of the spring motor that is provided in the cordless window shade.
Therefore, there is a need for a cordless window shade that has an improved drive system, and can address at least the foregoing issues.